I’ve always shied away from posting my finished amps because most folks here do such a tidy organised job that I never felt up to par.
But I wanted to share my finished 004. As an amp building approach I usually like to take inspiration from a bunch of designs (dumble, fender, etc) and amalgamate them together into an original design.
This in turn was my first attempt of doing a clone. My approach on this was to try to get as close to the original as far as parts selection, and I used 60’s Fender pots, 60’s piher resistors, NOS orange drops, mepco cathode resistors and the NOS large supply caps (blue sprague). The only “author’s” license was the cathode capacitors because I really love the yellow spragues vs the taiwanese used on the original. I had less room to wiggle as far as tweaks because I want to keep it close to the original, so I spent more time on the cabinet/speaker and NOS tubes department. I settled on a couple of RCA, Phillips, Mazda and Mullard I61 on the final tube roll and a large pine open back 1x12 with a vintage EVM 12S. Overall it was a good exercise to actually get to know the amp as is and spend time setting the knobs configuration to my taste. I don’t think it is a “voicing/topology” I would have chosen as I like the more gainy SSS amps, but it is a very nice amp in its own right and the more time I spend with it the more I like it.
This was my first time using eyelet boards, and probably the last. Although the final product looks much nicer, I find turrets a “tweakers” paradise compared to the eyelets which were cold sweat everytime I had to change something, specially because of the large leads from the vintage parts.
As far as the build itself I am using AN chassis and boards (which needed some modifications) and the FET board is from Erwin. The transformers are classic tone and I am using the 320-0-320 tap on PT. The back and faceplates were custom. It was a straightforward easy build, and took me far less time then the other experimental amps. The grounding scheme is as per Wonderland. The main challenge was to fit everything in the allocated space. In retrospect my only regret is the large footswitch socket (chosen mainly for aesthetics) which made my life a bit more miserable as far as space allocation of the LNFB on V1. I would have used a smaller one if I were to do it again.
My stumbling block was the PT interference with the reverb which has been discussed in this thread and I think it is good enough now.
The reverse speaker wiring was a must in this amp. I think it has to do with the mixer dry/wet tube.
Further discussions here:
https://ampgarage.com/forum/viewtopic.php?f=11&t=32935
As far as bias this amp likes it very cold, close to 50% and in line with the Two Rock manuals (which now make more sense to me)
Originally I wanted to add relays for FET and PAB but unless I gooped the preamp and added them on top (like two rock) there was no room. But I am haply as is.
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LTspice "says" that the higher the input impedance of the following stage the less efficient the parallel RC filter will cut bass.
You even tracked down that inductor too. I can tell that a tremendous amount of time went into that build. Very nice.